"It's come to our attention that our members who are speaking out in support of us on Facebook may be being targeted for doing so and are at risk of having sensitive information repeatedly published on other websites," it said.

"In order to protect yourselves, we recommend taking security precautions when speaking out on Facebook or abstaining from it altogether."

"On December 24th an unauthorized party disclosed personally identifiable information and related credit card data of some of our members," chairman George Friedman wrote.

We want [Bradley Manning] out on the streets at a fancy restaurant of his choosing, and we want this to happen in less than five hours'Anonymous' demand

"We have reason to believe that your personal and credit card data could have been included in the information that was illegally obtained and disclosed."

Mr Friedman said that a "leading identity theft protection and monitoring service" had been tasked with protecting clients. The company's email and servers have been taken offline.

The company also said the disclosure of what hackers claimed were "private clients" was "merely a list of some of the members that have purchased our publications and does not comprise a list of individuals or entities that have a relationship with Stratfor".

Splinter groups

A spokesperson alleging to represent Anonymous claimed they had been able to obtain the information because it was unencrypted.

They claimed that thousands of emails, passwords and credit card details had been taken.

They said Stratfor's clients included the US Department of Defense, law enforcement agencies and media organisations.

However, some confusion has surrounded the perpetrators of the attack. A release also claiming to come from the group on Christmas Day said that Anonymous did not carry out the attack, and in fact supported Stratfor due to its "unbiased" reporting work.

Image caption
Stratfor's site has been taken down for 'ongoing maintenance'

A message posted by Anonymous referring to the Stratfor attack read: "We hereby ask that Bradley Manning be given a delicious meal this Lulzxmas, and no, not the "holiday special" in the prison chow hall.

"We want him out on the streets at a fancy restaurant of his choosing, and we want this to happen in less than five hours."

The demand was not met.

At the time of publication, Stratfor could not be reached for comment.